It is well known to arrange telecommunications equipment in shelf assemblies. Circuit cards are removably connected to a backplane or midplane. The circuit cards are arranged in parallel to one another and are guided to be perpendicular to the backplane or midplane. Electrical connections are established between connectors on the backplane or midplane and complementary connectors on the back edge of each circuit card. Typically, the connectors include multiple pins and sockets arranged in one or more rows along part or all of the back edge of the circuit card. When a circuit card is inserted into the equipment shelf, the shelf guides provide an approximate alignment for the pins and sockets, and a precise alignment is achieved by the mating portions of the connectors.
The backplane or midplane typically provides power to each circuit card as well as electrical interconnections between circuit cards. The electrical signal assigned to each connector pin is left to the designer of the card and chassis to decide. Thus, various connector pin assignments, or pin-outs, have been developed, both industry standard and proprietary. For example, the PCI Industrial Computer Manufacturers Group (PICMG) 3.0 specification defines an open architecture whereby circuit cards from different manufacturers can interoperate within a shelf assembly. The PICMG specification defines the pinout and function of the various connectors used to connect a circuit card to the midplane of a shelf assembly.
FIG. 1 is a side view of the basic elements of a PICMG 3.0 compliant circuit card assembly. Front board 101 includes the electrical components required to perform a desired function or application and has connectors required to interface with the shelf backplane or midplane 103. The PICMG standard defines three connector zones. Zone 1 provides power connections and a shelf management interface, Zone 2 provides the data transport interface, and Zone 3 supports a user-defined input/output interconnect. Midplane 103 has connector interfaces for the Zone 1 and Zone 2 connectors. Rear transition module 105 provides user defined input and output connectivity between the Zone 3 connector on the front board 101 and external systems or devices.
Shelf assemblies permit the deployment of several application cards in a comparatively small space. In some instances, the electrical components required to perform a desired function cannot fit in the physical space allocated to a slot in a shelf assembly. This is particularly true in applications that require access to large databases, such as certain telecommunications applications, where an associated database is stored on a dedicated disk. In order to accommodate the dedicated disk, a single application card may occupy the physical space of two slots in the shelf assembly. The application card occupies one slot and interfaces with the midplane. The dedicated disk occupies the physical space of the adjacent slot, but may be mechanically supported by the application card and electrically connected to the application card rather than the midplane. In other implementations, the application card may occupy a single slot in the shelf assembly and the dedicated disk may occupy an adjacent slot. In this configuration, the dedicated disk may derive power from the midplane, but access from the associated application card is provided by an external cable. Both of these configurations require that the dedicated disk occupy a slot physically adjacent to the application card, which may not be possible in all situations. In addition, the external cable may cause undesired electromagnetic emissions as well as a potential connectivity failure point.
Accordingly there is a need to provide a system and method that allows access to an off-card storage device while not requiring that the off-card storage device be physically adjacent to the application card or connected using an external cable.